Vulnerability intelligence
CVE-2026-79611 and is rated Medium severity with a CVSS score of 5.5. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.
We have pushed updates to both the Early Access and Normal update channels of each of XenServer 8.4 and XenServer 9. We recommend that customers update to the latest version from their chosen channel following the instructions at https://docs.xenserver.com/en-us/xenserver/8/update or https://docs.xenserver.com/en-us/xenserver/9/update
For XSA-308 logic was introduced, as VMX VMEntry checks do not like the exact combination of state which occurs when #DB in intercepted, Single Stepping is active, and blocked by STI/MovSS is active, despite this being a legitimate state to be in. The resulting VMEntry failure is fatal to the guest.
Sadly there is another special sub-case of the above, with branch tracing enabled. In that case the prior adjustment would still cause a VMentry failure, as before fatal to the guest.
Source: NVD